Peter Knowlson, 59, pleaded guilty to falsely advertising 84 items of jewellery when they didn't have the appropriate hallmark.

He and his wife, Deborah Knowlson, 52, also falsely advertised the metallic purity of four other items of jewellery, and falsely described a three-stone diamond ring and a sapphire ribbon-designed ring as 18 carat.

The couple, who together own a 90 per cent share in Bayleaf Investments Ltd, trade as Cash Express and have three jewellery stores in Newland Avenue, Hessle Road, and Holderness Road in Hull as well as another one in East Yorkshire.

Officers from Trading Standards visited the different premises on November, 3, 2015, and discovered more than £25,000 worth of jewellery was being advertised for sale as 'precious metal items' with no hallmark.

Prosecutor Freddy Humphreys also said that four rings seized that were advertised online through Ebay under George James Jewellery were tested and found to be below the standard advertised.

Close-Up Of Gold Jewelry At Store For Sale (Image: Getty)

Three rings advertised as 18 carat were actually 16.7 carat, 14 carat, and 13.2 carat, while the fourth was advertised as 22 carat when it was only 8.47.

The defendants' lawyers argued no customers had been affected by the false advertising and that it was negligence on their part instead of dishonesty.

They also claimed jewellery was only a small part of their business and that neither knew about the provisions of the Hallmarking Act, but this was dismissed by Judge Mark Bury.

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"I do not accept that," he said. "Indeed their own sale documentation sets it out.

"It is inconceivable that these two defendants were not aware of the provisions of the Hallmarking Act.

"Miss Knowlson relied on a valuation report provided by an expert which she thought was sufficient enough to comply with the legislation.

"I do not accept that she was not aware of the legislation."

The couple started trading in 1994, but only began the jewellery side of the business in 2006. Deborah Knowlson took over the running of that part of the business in 2007.